1. Field of the Invention
The present invention relates generally to suspensions for supporting read/write heads over recording media. In particular, the present invention relates to a head suspension assembly with a strain transducer circuit thereon for detecting motion of the head suspension assembly out of a neutral position.
2. Description of the Related Art
Information storage devices typically include a read/write head for reading and/or writing data onto a storage medium such as a magnetic disk within a rigid disk drive. An actuator mechanism driven by a servo control is used to position the head at specific radial locations or tracks on the magnetic disk. Both linear and rotary type actuators are well known in the art. Between the actuator and the head, a head suspension is required to support the head in proper orientation relative to the disk surface.
The head suspension carries the read/write head so that the head can "fly" over the surface of the rigid disk while the disk is spinning. The head is typically located on a head slider having an aerodynamic design so that the head slider flies on an air bearing generated by the spinning disk. The combination of the head slider and the head suspension is referred to as a head suspension assembly. The head suspension includes a load beam which has a radius or spring section, a rigid region, and a flexure. The flexure is a spring or gimballing connection typically included between the head slider and the rigid section of the load beam so that the head slider can move in the pitch and roll directions of the head to accommodate fluctuations of the disk surface. The mounting region of the load beam is typically attached to an actuator arm which supports the suspension assembly over the rotating disk. A base of the actuator arm is coupled to an actuator.
When no external forces (with the exception of gravity) are acting on the head suspension assembly to deform it in any way, it is in a "neutral un-loaded" state. When the head is flying over the spinning surface of a disk, and is acted upon only by the force of the air bearing generated by the spinning disk, the head suspension assembly is in a "neutral loaded" state. However, the head suspension assembly can experience deformations that cause motion of the head away from either the neutral loaded or neutral un-loaded positions.
One way these deformations can occur involves a head suspension's tendency to bend and twist in a number of different modes, known as resonant frequencies, when driven back and forth at certain rates. Any such bending or twisting of a suspension can cause the position of the head to deviate from its neutral loaded or neutral un-loaded position.
Common bending and twisting modes of suspensions are generally known and discussed, for example, in the Yumura et al. U.S. Pat. No. 5,339,208 and the Hatch et al. U.S. Pat. No. 5,471,734. Modes which result in lateral or transverse motion (also known as off-track motion) of the head slider are particularly detrimental since this motion causes the head slider to move from the desired track on the disk toward an adjacent track. The three primary modes which produce this transverse motion are known as the sway, first torsion, and second torsion modes. The sway mode is a lateral bending mode in which the suspension bends in a transverse direction along its entire length. The first and second torsion modes are twisting modes during which the suspension twists about a rotational axis which extends along the length of the suspension.
Deformations of the suspension can also be caused by a secondary-actuation or microactuation device designed to move the head relative to the remainder of the head suspension assembly. Such a microactuation device is disclosed in U.S. patent application Ser. No. 08/457,432 filed Jun. 6, 1995 by Jurgenson et al. for a Head Suspension with Tracking Microactuator now U.S. Pat. No. 5,657,188.
Whether generated by motion during resonant modes, a secondary actuation device, or other causes, it can be useful to monitor motion of the head away from a neutral loaded or neutral un-loaded position, that is, read/write head off-neutral motion. Information about head off-neutral motion caused by undesirable resonant vibrations can be used to actively damp such vibrations. Further, monitoring of the displacement of the head caused by a first actuator can be important to correct placement of the head by a second actuator.